Raw materials of biological origin are potential sources of various biofuels or biofuel components. These raw materials can be converted to biofuels by feeding the raw material through a catalytic reactor by contacting it simultaneously with gaseous hydrogen. The resulting product is drawn off the reactor as a product stream which can be further fractionated for example by distillation to form biofuel/biofuel components.
There are however various problems related to production processes of biofuels from the raw materials of biological origin, such as poisoning and clogging of the catalyst material used in the production processes. There are impurities in the raw materials of biological origin, such as metals and solids that cause the inactivation of the catalyst material and prevent it to function properly. In order to prevent the inactivation of the catalyst and to prolong its lifetime, the raw material can be purified and/or pretreated before feeding it to the hydrotreatment process. Purifying of the raw materials of biological origin to be suitable for feeding to a catalytic process is also challenging. Prior art describes various ways of doing this. However, these all have problems and the quality of the raw material is not always in required level for the catalytic step to be able to function in the most efficient way.
One possibility of purifying and/or pretreating a raw material of biological origin to be fed to catalytic hydrotreatment processes is ion-exchange with an acidic ion exchange resin. Another possibility is to use methods such as adsorption on a suitable material, ion exchange, or acid washing to remove alkaline metals and earth alkaline metals (Na, K, Ca). Yet another possibility is to use degumming for removing metals in the feed. Degumming is performed by washing the biological feed at 90-105° C., 300-500 kPa(a), with H3PO4, NaOH and soft water and separating the formed gums. A major amount of metal components, which are harmful for the hydrotreatment catalyst, are removed from the feedstock during the degumming stage.
If the raw material of biological origin contains tall oil, depitching of the crude tall oil can be used to remove impurities from the tall oil. Depitched tall oil is obtained by evaporating crude tall oil, for example by thin-film evaporator. U.S. Pat. No. 5,705,722 describes converting unsaturated fatty acids, for example tall oil fatty acids to naphtha and cetane improvers for diesel fuels. According to the document, a feedstock comprising tall oil is fed through a hydrodeoxygenating reactor containing NiMo/CoMo catalyst where it is contacted with gaseous hydrogen. The resulting product is drawn off the reactor as one product stream which is further fractionated by distillation, to naphtha and middle distillate which is said to be used as a cetane improver. Also a residue is drawn off from the reactor. However, this process has disadvantages, for example the yield of biofuel or biofuel components, i.e. naphtha and cetane improvers, is poor. This is due to the fact that in depitching a huge amount of valuable raw material for hydrogenation is lost as residue, i.e. pitch. According to the document, the residue is used as such as fuel for boilers.